1. Field of the Invention
The present invention relates to a displacement difference-absorbing mechanism for a cylinder apparatus, the displacement difference-absorbing mechanism being capable of absorbing a displacement difference generated between a displacement-transmitting member and a displacement member that is displaceable along a main cylinder body. The displacement difference-absorbing mechanism further is capable of suppressing loads applied from the displacement member to the displacement-transmitting member.
2. Description of the Related Art
A cylinder apparatus such as a rodless cylinder has been used as a means for transporting a workpiece. The cylinder apparatus includes a piston, which is displaceable within a main cylinder body, and wherein a piston yoke, which is connected to the piston, is exposed to the outside through a slit formed on an upper portion of the main cylinder body. A slider is integrally installed on the piston yoke. The slider is displaced in the axial direction of the main cylinder body due to displacement of the piston, in order to transport the workpiece.
In the rodless cylinder described above, when a load (for example, a pressing force) is applied to the slider, for example, by a workpiece, then the piston becomes inclined due to the load, and a nonuniform load is exerted on the piston seal and the piston. As a result, air leakage and/or an increase in sliding resistance is brought about in the rodless cylinder, as a result of the displacement difference caused by the load. It is impossible to smoothly displace the slider in the axial direction in some cases.
In view of the above, a rodless cylinder has been suggested, which is provided with a displacement difference-absorbing mechanism that is capable of absorbing the displacement difference generated between the slider and the piston yoke. The rodless cylinder comprises a disk-shaped bearing, which is provided between a guide element that functions as the slider and a load-transmitting element that applies the displacement load. The guide element is retained rotatably within a substantially horizontal plane about the central axis of the bearing. Further, the guide element is displaceable a predetermined amount in a vertical direction with respect to the bearing. More specifically, in this arrangement, a displacement difference, which is generated on the guide element and the load-transmitting element when a load is applied to the guide element, is absorbed by displacement of the guide element with respect to the bearing (see, for example, Japanese Laid-Open Patent Publication No. 60-234106).
However, in the case of the displacement difference-absorbing mechanism disclosed in Japanese Laid-Open Patent Publication No. 60-234106, when a displacement difference is generated in relation to the guide element, the mechanism can only absorb displacement differences that occur in a vertical direction, substantially perpendicular to the displacement direction of the guide element, and in a rotational direction centered about the vertical direction.
Another displacement difference-absorbing mechanism, which is provided externally of a rodless cylinder, as disclosed in Japanese Patent Publication No. 7-1041, is constructed in the following manner. That is, a circular arc-shaped surface, which is formed on an engaging projection, makes line-to-line contact with an abutment tab connected to both end surfaces of a slider, wherein the displacement difference is absorbed by displacement of the slider about the center of the abutment portion. However, in the case of the rodless cylinder disclosed in Japanese Patent Publication No. 7-1041, the contact area between the circular arc-shaped surface and the abutment tab is small. Therefore, it is difficult to handle large loads in the displacement direction.
In order to solve the aforementioned problems, the present applicant has proposed a displacement difference-absorbing mechanism for a rodless cylinder, in which it is possible to absorb displacement differences brought about in a horizontal direction, substantially perpendicular to the displacement direction of a slider that is provided outside the rodless cylinder, as well as in a rotational direction about the center of the displacement direction of the slider. Further, the mechanism is responsive even when large displacement differences are generated (see Japanese Laid-Open Patent Publication No. 11-93908).
As shown in FIG. 13, the rodless cylinder comprises a movable member 2, which is provided on an upper surface of a cylinder tube 1, and which is displaceable in the axial direction. A displacement difference-absorbing mechanism 3 is provided at both ends of the movable member 2. The displacement difference-absorbing mechanism 3 comprises a pair of end covers 5a, 5b, which are fixed to respective ends of a slider 4 formed integrally with the movable member 2, and a pair of couplers 8a, 8b, each of which has a circular arc-shaped curved surface section 6 disposed on one side surface thereof, and a flat section 7 disposed on the other side surface. The couplers 8a, 8b are positioned with respect to the movable member 2 through the aid of plate-shaped stoppers 9a, 9b. The couplers 8a, 8b are slidably inserted, in a state in which the curved surface sections 6 of the couplers 8a, 8b make surface-to-surface contact with recesses 10 provided in the end covers 5a, 5b. 
When a displacement difference is generated in the horizontal direction substantially perpendicular to the displacement direction of the movable member 2, or when a displacement difference is generated in the rotational direction about a central vertical line, the couplers 8a, 8b are slidably displaced through contact surfaces of the stoppers 9a, 9b, which are provided between the couplers 8a, 8b and the movable member 2, and thus the displacement difference generated in the movable member 2 is absorbed.
In the case of the displacement difference-absorbing mechanism described above, a large number of parts is required, and the structure of the displacement difference-absorbing mechanism is complicated. Further, it is difficult to install the displacement difference-absorbing mechanism on the rodless cylinder.